Contemporary public health questions concern physical activity and cancer incidence. Recent epidemiological evidence has associated sedentary work and leisure-time activities with increased risk of colon and breast cancer; and long-time suspicion links overweight and endocrine patterns with colon, breast, prostate, and other cancers. Unique databases offer opportunities to study these questions among 25,000 U.S. college alumni and 6,000 San Francisco Bay Area longshoremen. Lifestyle and personal characteristics -- e.g. sedentariness of work and leisure time, and increased body weight-for-height -- would be examined for relationship to incidence, of non-fatal and fatal cancers of the colon, rectum, prostate, and perhaps such others as the pancreas, lung, and breast. Proven resources include: 1) College student data of 1916-1950 from physical examination, social, and athletic records; 2) contemporary alumni data since 1962 on the same study subjects from mail questionnaire responses pertaining to exercise, other lifestyle elements, personal health, and family disease patterns; and 3) mortality certification. Also: 4) longshoremen data from multiphasic health examinations; 5) annual job classifications of these workers; and 6) their death certificate assessments. A projected questionnaire would update the alumni follow-up to 23 years, while survey of annual job assignments would extend the longshoremen follow-up to 34 years. Multivariate analyses would examine absolute measurements and changing patterns of physical activity, body size, and other lifestyle characteristics. Subjects would be classified as to physical activity by type, frequency, intensity, duration, kilocalorie expenditure, and postural nature (sitting, standing, and locomotion). Expected numbers of cancer cases offer statistical power sufficient to test hypotheses of physical activity and body size as causation for cancers of the colon, rectum, and prostate. Within these two diverse populations, differences in physical activity, body size, cigarette habit, blood pressure level, etc. significantly altered incidence of cardiovascular-respiratory diseases and estimates of longevity. Those findings invite parallel study of cancer risk, especially since much of the information gained thus far has been applicable to public health.